Printing apparatus

ABSTRACT

Printing apparatus is disclosed in accordance with the teachings of the present invention wherein a plurality of applicators capable of retaining electrostatic developer particles are mounted in spaced relationship on movable support means such that said applicators sequentially contact an electrostatic latent image to deposit said electrostatic developer particles thereon. In one embodiment of the present invention the movable support means comprises a transparent rotatable cylinder. In another embodiment of this invention the movable support means comprises an endless belt movable about a plurality of cylinder means.

United States Patent [19 Ring I Nov. 13, 1973 PRINTING APPARATUS [75] Inventor: Howard D. Ring, Rochester, NY.

[73] Assignee: Xerox Corporation, Stamford,

Con -M [22] Filed: Dec. 30, 1971 [21] App]. No.: 214,300

[52] US. Cl. 101/1, 101/DIG. 13, 118/637, 346/74 ES [51] Int. Cl. G01d 15/12 [58] Field of Search 101/1, DIG. 13; 118/637, DIG. 33; 117/17.5; 346/74 ES [56] References Cited UNITED STATES PATENTS 2,846,333 8/1958 Wilson IOIIDIG. 13 2,985,135 5/1961 Hickerson.... 118/637 X 3,045,587 7/1962 Schwertz... 101/D1G. 13 3,140,199 7/1964 York..... 118/637 3,152,012 10/1964 Schaffert 118/637 Walkup l01/DIG. l3 Gundlach et a1. 118/637 X Primary Examiner-Edgar S. Burr Attorney-James J. Ralabate et a1.

[57] ABSTRACT Printing apparatus is disclosed in accordance with the teachings of the present invention wherein a plurality of applicators capable of retaining electrostatic developer particles are mounted in spaced relationship on movable support means such that said applicators sequentially contact an electrostatic latent image to deposit said electrostatic developer particles thereon. In one embodiment of the present invention the movable support means comprises a transparent rotatable cylinder. In another embodiment of this invention the movable support means comprises an endless belt movable about a plurality of cylinder means.

13 Claims, 6 Drawing Figures Fig.1

PATENIEDNBY'I 3 I913 3.771.184

. SHEET 10F 3 Fig. 4.

PATENTEBnuv 13 I975 SHEET 2 [if 3 1 v PRINTING APPARATUS This invention relates to printing apparatus and in particular to apparatus for developing an electrostatic latent image.

In the printing arts, one of the major categories of printing apparatus that has been developed may be classified as impact printers. Conventional impact printers require hammer means to strike a selected character embodied in a character matrix, which selected character is forced into contact with a recording medium, thereby printing a character. Impact printing techniques are exemplified by slow speed,-shock and vibration caused by hammer movement, and excessive wear on the mechanical components. Nevertheless impact printers are widely utilized in conventional keyboard actuated printing devices such as typewriters, teletypewriters, computer read-in and read-out devices, calculating machines, line printers, and the like.

In recent years a new technique of printing has been developed wherein a character pattern of electrostatic charges is deposited upon a medium to form an electrostatic latent image which electrostatic latent image is developed by the deposition of developer particles thereon. This technique is embodied in the commercial process known as electrophotography wherein the aforementioned electrostatic latent image is produced by selectively dissipating a uniform layer of electrostatic charges by imaging modulatedradiant energy thereon. Electrophotography has been utilized in document reproducing machines such as that described in U.S. Pat. No. 3,301,126 which issued to R. F. Osborne et al. on Jan. 31, 19.67 and assigned to Xerox Corporation, the assignee of the present invention. Electrophotography has also been utilized in photoprinting systems such as described in U.S. Patent application Ser. No. 887,666 filed on Dec. 23, I969, now US. Pat. No. 3,693,517.

' The aforementioned printing technique has found application in electrography systems wherein the electrostatic charges are deposited on a recording medium by conductive, electrically-biased electrodes or styli. Electrography systems have been utilized as high speed computer read-out devices, teletypewriter receivers, facsimile receivers, and the like.

An attendant disadvantage of prior art electrostatic printing systems such as electrophotographic photoprinting systems and conventional electrography systems is the inability of an operator to visually perceive a character immediately after the recording thereof. The apparatus heretofore utilized by the prior art for developing an electrostatic latent image obstructs the field of view of an operator during the developing process such that an entire line or a plurality of lines of images must be developed before visual examination thereof is obtained. Accordingly, an operator of a. keyboard actuated electrostatic printing device will not be cognizant of errors, such as typeographical errors, until well after such errors are committed and the character is recorded. Thedelay between the recording of information and detecting same tends to limit the speed at which characters are recorded, resulting in inefficient operation of such electrostatic printing devices. This has been a criticalfactor in attenuating enthusiastic reception of keyboard actuated electrostatic printing devices that may be utilized as typewriters, teletypewriter transmitters, computer input terminals, and the like.

Therefore, it is an object of the present invention to provide apparatus for developing an electrostatic latent image.

It is another object of the present invention to provide apparatus for recording characters on a print receiving surface wherein each character may be visually examined immediately after the recording thereof.

It is a further object of this invention to provide apparatus for use in an electrostatic printing device wherein a character pattern comprised of electrostatic charges is viewed immediately after the development thereof.

Yet another object of this invention is to provide printing apparatus operable at relatively high speeds which permits immediate visual detection of a printed character.

A still further object of the present invention is to provide apparatus for developing and viewing an electrostatic charge pattern.

There are other objects and advantages of the invention which will become clear from the following detailed description of exemplary embodiments thereof and the novel features will be particularly pointed out in connection with the appended claims.

In accordance with this invention, apparatus for developing an electrostatic latent image is provided wherein a plurality of applicators capable of retaining electrostatic developer particles are mounted in spaced relationship on movable support means such that said applicators sequentially contact the electrostatic latent image to deposit said electrostatic developer particles thereon. A first exemplary embodiment hereof contemplates a transparent cylinder for utilization as a movable support means; and a second exemplary embodiment contemplates the use of an endless belt movable about a plurality of cylinder means as a movable support means.

The present invention may be utilized with an electrophotographic device such as a document reproducing device, wherein electrostatic latent images are formed by imaging modulated radiant energy onto a charge surface. The present invention may also be utilized with electrographic devices wherein said electrostatic latent images are formed by selectively energizing electrode means disposed in the vicinity of a dielectric surface. The electrostatic printing devices with which the present invention may be utilized are adapted to be controlled by any convenient source of data such as an actuatable keyboard, an original document to be reproduced, a digital computer or the like. The invention will be more clearly understood by reference to the following detailed description of exemplary embodiments thereof in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of one embodiment of the present invention; I

FIG. 2 is a perspective view of the present invention as utilized with an electrographic device;

FIG. 3 is a sectional view taken along line 3-3 of FIG. 1;

FIG. 4 is a front elevational view of the embodiment illustrated in FIG. 1;

FIG. 5 is a side elevational view of another embodiment of the present invention; and

FIG. 6 illustrates a modification of the embodiment illustrated in FIG. 5 therefor.

Referring now to the drawings wherein like reference numerals are used throughout, and in particular to FIG.

1, there is illustrated a perspective view of apparatus for developing and viewing an electrostatic latent image comprising movable support means 11 and applicators l2 14. Movable support means 11 comprises a transparent cylinder rotatable about the longitudinal axis thereof in the direction indicated by the arrow A. The transparent cylinder may be comprised of suitable material such as glass, plastic or the like. Alternatively, the movable support means 11 need not be transparent but may comprise a plurality of radially extending frame structures or ribs having a common intersection along a longitudinal axis and disposed in cylindrical configuration. The frame structures may be made of suitable material such as glass, plastic, aluminum or the like. However, it will be understood that the terminology transparent cylinder as used herein refers equally to this configuration. Each of applicators 12, 13 and I4 is capable of retaining conventional electrostatic developer particles that may be applied thereto. Such electrostatic developer particles are known as toner particles and are adapted to exhibit an electrostatic charge. The toner particles may exhibit a positive or negative charge for a purpose soon to be described. Those of ordinary skill in the art will recognize that such toner particles may consist of a pigmented resinous powder. Alternatively the toner particles may be dispersed in an insulating liquid.

The applicators 12, 13 and 14 are preferably comprised of fibrous brushes which may be made from materials such as natural fur (beaver, rabbit or the like) or other materials described in US. Pat. No. 3,251,706 which issued to L. E. Walkup on May 17, 1966 and assigned to Xerox Corporation. Hence, triboelectric attraction is maintained between the applicators and the electrostatic developer particles. As illustrated in FIG. 1, each fibrous brush includes a longitudinal dimension and the brush is mounted on the surface of the transparent cylinder by suitable fastening means, such as cement, such that said longitudinal dimension is substantially parallel to the axis of rotation of the cylinder 11. If desired, however, the fibrous brushes may be mounted in a slightly skewed relationship. The mounted fibrous brushes 12, 13 and 14, which include substantially identical physical dimensions, exhibit a spaced relationship whereby substantially equal angles are defined between successive fibrous brushes. Thus, the angle between brushes l2 and 13 is equal to the angle between brushes 13 and 14 which, in turn, is equal to the angle between brushes 12 and 14. It should be noted that the lateral dimension of each brush, i.e., the width thereof, need not be equal to the spatial separation between successive brushes. The fibers of each of the fibrous brushes 12 14 extend in a radially outward direction from the transparent cylinder 11.

In operation, the cylinder 11 is rotated by suitable driving means coupled theretosuch as an electric motor, whereby applicators l2 14 are correspondingly rotated. The rotation of the cylinder 11 may be continuous or, if desired, a stepped rotation may be imparted thereto. As the applicators 12 1.4 rotate, they will s e- I quentially contact an electrostatic latent image formed of electrostatic charge patterns on a print receiving surface. The print receiving surface may be disposed in tangential relationship with respect to the cylindrical surface defined by the terminal points of the fibers included in the applicators. As is understood the toner particles retained by the applicators will exhibit a polarity opposite to that of the electrostatic charge patterns. Consequently, when an applicator contacts an electrostatic charge pattern the toner particles will be electrostatically attracted to the charge pattern, which electrostatic attraction is greater than the triboelectric attraction between the toner particles and the brush fibers. Hence the toner particles are deposited on the electrostatic charge patterns to develop the electrostatic latent image. The applicators 12 14 may be resupplied with toner particles by conventional means such as a donor surface, a sump, or a liquid reservoir.

The transparent cylinder does not present a visual obstruction to an optical path passing therethrough. It is recognized that as the cylinder 11 and applicators l2 l4 rotate, an optical path passing through the transparent cylinder to a developed image will be periodically interrupted. The periodic interruption of the optical path will produce a flickering effect; however the human eye will not discern this effect if the transparent cylinder 11 is rotated at an appropriate speed. Hence, an observer positioned along said optical path may immediately perceive the developed image. For purposes of explanation it may be seen from FIG. 1 that the optical path passing through the transparent cylinder 11 may be interrupted by applicator l4 and then by applicator 12. The maximum number of interruptions during each rotation of the transparent cylinder 11 is, depending upon the width of each applicator, equal to twice the number of applicators mounted on cylinder 11. Hence, it is desirable to limit the total number of applicators mounted on the transparent cylinder 11 to a-reasonable number such as three or four so that the flickering effect does not become objectionably noticeable to an observer. The three applicators illustrated in FIG. 1 are therefore understood to be merely exemplary and are not intended to limit the present invention. Favorable results have been obtained wherein one applicator has been mounted on the cylinder.

The electrostatic latent image developed by the apparatus illustrated in FIG. 1 may be supported by photoreceptor means such as a conventional electrophotographic member adapted to have an electric charge deposited thereon and to have said charge dissipated in accordance with radiant energy transmitted thereto. Accordingly, the electrophotographic member may comprise amorphous selenium or a photoconductive pigment binder layer overlying a conductive support surface in drum, belt or web configuration. The longitudinal dimension of each of applicators 12, 13 and 14 may therefore be coextensive with the longitudinal axis of the electrophotographic drum or the lateral dimension of the electrophotographic belt or web. It is, of course, understood that applicators l2 14 and cylinder 11 may assume any convenient length to accommodate the particular application thereof. Alternatively the electrostatic charge developed by the apparatus of FIG. 1 may be supported by a conventional electrographic member such as an insulating recording medium. The insulating recording medium may be comprised of a plastic coated paper, pre-dried paper, or any other dielectric sheet having a sufficiently high resistance to retain an electrostatic charge pattern. The insulating recording medium may adopt one of the aforementioned geometric configurations such as a drum, an endless belt or a web, or may be formed of pre-cut sheets. The electrostatic charge supported by the insulating recording medium may be deposited thereon by selectively energizing an electrographic stylus, which stylus may be comprised of a matrix array of electrodes.

Referring now to FIG. 2 there is illustrated one embodiment of the present invention which may be utilized in an electrostatic printing device, and comprises the apparatus of FIG. 1 including transparent cylinder 11 and applicators l2 l4, insulating recording me-.

dium 21, electrode means 22, electrographic stylus 24, and a source of motive power 30. The transparent cylinder 11 is understood to be a continuous structure; however to facilitate the explanation of the applicability of the present invention to an electrostatic printing device the transparent cylinder 11 is diagrammatically illustrated in broken configuration. The insulating recording medium 21 may be comprised of a base paper which is electrically conductive and which is coated with a dielectrical plastic having avery high resistivity. The insulating recording medium 21 is supported by electrode means 22 and guide support member 23, and is adapted to be advanced in the direction indicated by the arrow B. Electrode means 22 serves as a base electrode and supports the insulating recording medium 21 in close proximity to the electrographic stylus 24.

Electrode means 22 includes a surface portion 221 adapted to maintain the insulating recording medium 21 in a plane parallel to the surface of electrographic stylus 24 and parallel to the longitudinal axis of transparent cylinder .11.

The electrographic stylus 24 may include a matrix array of parallel conductive electrodes suitably isolated electrically from each other. The matrix array of conductive electrodes may be pin electrodes supported by insulating supportmeans 25 through which electrical conductors may be provided to each of the pin electrodes for the selective energization thereof in response to electrical recording signals. The electrical signals supplied to the conductors may be generated by the actuation of a keyboard, by the receipt of facsimile signals, or by any suitable source of data signals. insulating support means 25 is adapted to support the electrographic stylus 24 at a suitable distance from the insulating recording medium 21 such that air ionization may occur in the air gap between the electrographic stylus 2 4 and the surface of the insulating recording means 21, whereby a small electrical discharge may be established between the selectively energized electrodes and the electrode means 22. Suitable distances that have heretofore. been utilized are within the range 3 to 5 thousandths of an inch between the electrodes.

To facilitate the recording of a line of characters, relative lateral displacement must exist between the insulating recording medium 21 and the electrographic stylus 24. Accordingly insulating support means 25 may be displaced by a suitable motor, not shown, which may be a constant drive motor or a conventional stepping motor. Additional means may be provided for returning the insulating support means 25 from a rightmost position to a leftmost position after the recording of a complete line of characters. One example -of suitable drive means is described in U.S. Patent application Ser. No. 805,694 filed on Mar. 10, 1969 and assigned to Xerox Corporation. Alternatively, the insulating support means 25 may remain fixed, and electrode means 22 and guide support member 23 may form a conventional movable carriage adapted to transport the insulating recording medium 21 in a right to left direction,

thereby enabling the electrographic stylus 24 to record successive characters thereon.

The transparent cylinder 11 is positioned such that each of applicators 12, 13 and 14 mounted on the transparent cylinder may be rotated into contact with the surface of the insulating recording medium 21. Hence, the insulating recording medium may exhibit a tangential relationship with respect to the cylindrical surface defined by the terminal points of the fibers included in the applicators. The electrographic stylus 24 is interposed between the insulating recording medium 21 and the' transparent cylinder 11. It is understood however, that when the applicators l2 14 rotate into the vicinity of the electrographic stylus 24 the fibers of each of the applicators are deformed by the insulating support means 25 to permit rotation therepast, and no interaction occurs between the charged electrostatic developer particles retained by the applicators and the electrodes included in the electrographic stylus. A shaft 26 is suitably fastened to the transparent cylinder 11 and is supplied with a rotational torque by the source of motive power 30. The source of motive power 30 may comprise a conventional electric motor which may be a constant drive motor or a conventional stepping motor. Conventional coupling means comprised of endless belt 27 deployed about rollers 28 and 29 may be utilized to couple the motor 30 to the shaft 26. Other mechanical coupling means such as drive speed reducing gears may be utilized if desired. It is preferable that the rotational speed of electric motor 30 be maintained at a constant value notwithstanding the loading effects produced when an applicator rotates into the vicinity of insulating support means 25.

Although not illustrated in FIG. 2 it is understood that a source of electrostatic developer particles is provided to supply the applicators 12 14 with electrostatic developer particles subsequent to the deposition of such particles upon an electrostatic charge pattern. The source of electrostatic developer particles may be similar to that described in the aforementioned U.S. Patent application Ser. No. 805,694 or may comprise suitable liquid dispersion apparatus well knwon to those of ordinary skill in the art.

The operation of the electrographic recording device illustrated in FIG. 2 incorporating the present invention will now be described. Electric motor 30 imparts a rotational velocity to the transparent cylinder 11 such that the transparent cylinder 11 rotates in the direction indicated by the arrow A about the longitudinal axis thereof. Electrostatic developer particles are applied to each of applicators 12 14 by a source of particles not shown. The fibers included in each of the applicators serve to charge the supplied electrostatic developer particles whereby the particles are retained by triboelectric attraction to the applicators. Electrostatic developer particles will be supplied to those applicators and portions of applicators which are deficient in particles. Consequently, the consideration of non-uniform loading of an applicator, i.e., excess electrostatic developer particles supplied to an applicator, is obviated.

Electrographic stylus 24 is proximately situated with respect to the dielectric coating of insulating recording means 21 and the conducting surface of insulating recording means 21 is in intimate contact with the surface 221 of electrode 22. The electrographic stylus 24 is selectively energized by applying data signals thereto such as by depressing a selected key of a keyboard, by

supplying received facsimile signals thereto, or the like. The. selective energization of electrographic stylus 24 establishes corresponding electrical discharges between each of the selectively energized electrodes included in the elcctrographic stylus 24 and electrode means 22. Accordingly, ions which are created in the air gap between the electrographic stylus 24 and the surface of insulating recording means 21 are deposited on the surface of the insulating recording means 21 in a pattern corresponding to the selectively energized electrodes. Thus an electrostatic latent image comprised of an electrostatic charge pattern is formed. The polarity of the electrostatic charge pattern may be positive or negative, however it should be noted that said polarity should be opposite to that of the electrostatic developer particles retained by the applicators 12 14. After forming an electrostatic latent image the electrographic stylus 24 supported by insulating support means 25 is displaced a suitable amount in preparation for the recording of a subsequent image. Alternatively the carriage assembly comprised of electrode means 22 and guide support means 23 may be displaced to prepare the insulating recording means 21 for reception of a subsequent electrostatic latent image.

The electrostatic latent image formed on insulating recording means 21 is developed to form a visible image when one of applicators 12 14 rotates into contact therewith. It should be understood that when an applicator sweeps over an electrostatic charge pattern the electrostatic force exerted on the electrostatic developer particles is sufficient to overcome the tribeelectric attraction between the developer particles and the fibers of the applicator to thereby urge the particles into contact with the charge pattern. It may be observed that the forces exerted on the electrostatic developer particles by the impact between an applicator and the surface of the insulating recording means 21 may be sufficient to dislodge said particles from the applicator. The electrostatic developer particles however, will be attracted only to an electrostatic charge pattern. Thus, if the insulating recording means 21 supports a developed image, or if an electrostatic latent image is not present the dislodged electrostatic developer particles will merely cascade across the surface of the insulating recording medium 21 to be recovered by a sump located beneath the illustrated apparatus. Thus in accordance with the configuration illustrated in FIG. 2 if the characters C, D", E have been previously developed and the character F is an electrostatic charge pattern deposited on the, surface of the insulating recording medium 21 by selectively energized electrographic stylus 24, electrostatic developer particles retained by the fibers of applicator 12 will be removed therefrom to develop the image of the character F. Other electrostatic developer particles will be removed from applicator 12 in the vicinity of the developed images of characters C, D" and E. However insufficient electrostatic forces will exist between the developed images and said other removed electrostatic developer particles, and the electrostatic developer particles will fall, under the influence of the gravitational forces exerted thereon, to a sump for subsequent recovery thereof. One of ordinary skill in the art will recognize that an insulating support means 25 is displaced in a left to right direction, successive portions of the applicators 12 14 will deposit the electrostatic developer particles retained thereby onto the electrostatic charge patterns formed by the electrographic stylus 24. In addition, successive portions of the fibers of each applicator will be deformed by the presence of the insulating support means 25. Thus each applicator is subjected to uniform wear along the entire length thereof.

However, if the carriage assembly comprised of electrode means 22 and guide support means 23 is displaced in a right to left direction, that portion of each applicator extending to the right of insulating support means 25 is not utilized to'develop an electrostatic charge pattern; and each applicator is not subject to uniform wear along the entire length thereof. However, this may be overcome if desired by displacing transparent cylinder 11 and each of applicators 12 14 mounted thereon in a right to left direction in synchronism with the displacement of the carriage assembly. Alternatively, that portion of cylinder 11 extending to the right of insulating support means 25 may be omitted.

It may now be seen that an optical path may be established from an observer to a developed image through the transparent cylinder 11. The observer may be the operator of a keyboard adapted to be utilized with the apparatus illustrated in FIG. 2. Thus, each character may be perceived immediately after the recording thereof and it is not necessary to record a plurality of lines of characters before observation of a first recorded line of characters is obtained. It is noted that an entire line of recorded characters may be visually perceived if the longitudinal dimension of each of applicators l2 14 is aligned in parallel relationship with respect to the longitudinal axis of the transparent cylinder 11. If however it is preferred not to observe an entire line of characters, the longitudinal dimension of each applicator may exhibit a skewed relationship with respect to the axis of transparent cylinder 11. One advantage of mounting a plurality of applicators on the transparent cylinder 11 is that improved development of electrostatic images obtains. For example if the character D is not adequately developed by the deposition of electrostatic developer particles thereon by the applicator 12, additional electrostatic developer particles may be deposited thereon by applicators l4 and 13 until a suitable developed image is obtained. Although satisfactory development of a recorded electrostatic latent image may be realized by a multiplicity of applicators mounted on the transparent cylinder 11, it is recalled that the flickering effect by which an observer may perceive the recorded characters becomes objectionably noticeable if an inordinate amount of applicators is utilized. It is preferred that the axial length of transparent cylinder 11 and therefore the longitudinal dimension of each of applicators l2 14 be at least coextensive with the lateral dimension or width, of the insulating recording medium 21 such that satisfactory development of the electrostatic charge patterns may be achieved. I

After development, the electrostatic developer particles may be fixed to the insulating recording medium 21 in any of several conventional manners. For example, guide support means 23 may include a conventional heating assembly through which the insulating recording medium 21 is advanced. The heating assembly may fuse the electrostatic developer particles to the surface of the insulating recording medium 21 in the well-known manner. Flash fushing or fixing may also be used to render the developed images permanent.

It should be recognized by those of ordinary skill in the art that the electrostatic charge patterns may be deposited on the surface of the insulating recording medium 21. by conventional means other than the electrographic stylus 24 illustrated herein. For example, a linear array of energizable light emissive elements may be disposed to selectively dissipate a uniform layer of electrostatic charge deposited on the surface of the insulating recording medium 21. The insulating recording medium may comprise a conventional electrophotographic member and the linear array of light emissive elements may be selectively energized in accordance with data signals supplied thereto. In addition the light emissive elements may be positioned in a manner that does not interfere withthe optical path established between an observer and a recorded character, which optical path passes through the transparent cylinder 11.

Turning now to FIG. 3 there is illustrated a sectional view of the apparatus in accordance with the present invention taken along lines 3-3 of FIG. 1. FIG. 3 additionally illustrates electrographic stylus 24 mounted on insulating support means 25. It is seen that the electrographic stylus 24 is dis posed in advance of transparent cylinder 11. Thus as each of applicators 12 14 rotates into the vicinity of electrographic stylus 24, the fibers included in each applicator tend to be deformed and exhibit a surrounding relationship with respect to the electrographic stylus; Nevertheless, the fibers do not interfere with the surface of the electrographic stylus so as to impede the ionization of the air gap existing between the stylus and the surface of an insulating recording medium positioned opposite thereto. F IG.- 3 further illustrates that an optical path represented by the arrow C extends from an observer through the transparent cylinder 11 to a recorded character. As hereinbefore explained, the rotation of applicators l2 14 in the direction indicated by the arrow A results in periodic interruption of the established optical path. However, the rotational velocity of cylinder 1 l and the number of.applicators mounted thereon may besuitably chosen so that the consequential flickering effect is imperceptible.

FIG. 4 is a front view of the apparatus illustrated in FIGS. 1 and 2 when the angular position depicted by FIG. 3 is obtained. The characters C, D E recorded on insulating recording medium 21 may be visually observed through the transparent cylinder 11. An electrostatic charge pattern deposited on the insulating recording medium 21 by the electrographic stylus mounted on insulating support means 25 may be observed as a viewable image when an applicator such as applicator 13 passes over the charge pattern, and then rotates into a position beneath the line of characters. Thus it is seen that continuous rotation of the applicators l2 14 produces a developed image and enables immediate perception of said developed image by an observerv It should now be understood that the flickering effect caused by the periodic interruption of the optical path between an observer and the recorded characters is not readily perceptible by the human eye.

Another embodiment of the presentinvention is illustrated in FIG. 5 which comprises an endless belt 51 deployed about cylinder means 55 and 56, and applicators 52, 53, 54 The endless belt 51 is adapted to be moveable about cylinder means 55 and 56 in the direction indicated by the arrow B and therefore, a conventional source of motive power may be coupled to one of the cylinder means to impart a rotational velocity thereto. The endless belt 51 may comprise a transparent conveyor belt having a uniform surface. Applicators 52, 53, 54 are similar to aforedescribed applicators 12 14 described with respect to FIGS. 1 4. Accordingly each of the applicators illustrated in FIG. 5 may comprise elongated fibrous brushes suitably fastened to the endless belt 51 as by cement. The fibrous brushes are mounted on the endless belt 51 in spaced relationship wherein the longitudinal dimension of each fibrous brush is substantially perpendicular to the direction of motion of endless belt 51. It will be observed therefore, that the fibrous brushes exhibit a substantially parallel relationship with respect to the longitudinal axis of each of cylinder means and 56. It is preferred that the applicators are mounted on the endless belt 51 such that substantially equal spaces are defined between successive applicators, however it is not necessary that the'width of each applicator be equal to each defined interspace. Each of the applicators 52, 53 54 may be made from materials described in US. Pat. No. 3,251,706 which issued to L. E. Walkup. The applicators include fibers extending in a normally outward direction from the surface of the endless belt 51 such that the terminal points of the fibers define a plane parallel to the surface of the endless belt. The endless belt 51 may be a transparent endless belt made from glass, plastic or the like and if desired, cylinder means 55 and 56 may comprise transparent cylinders made of glass or plastic. An alternative embodiment of endless belt 51 may comprise a pair of support members deployed about the opposite end portions of cylinder means 55 and 56. The support members are adapted to receive applicators 52, 53, 54 mounted thereon and may comprise a pair of moveable chains, a pair of moveable cables or a pair of relatively thin belts. It should be apparent that if the endless belt 51 is comprised of a transparent belt or a pair of oppositely disposed support members an optical path may be established therethrough such that the apparatus illustrated in FIG. 5 may be readily applied in the manner depicted in FIG. 2.

In operation a suitable source of motive power, such as a constant drive motor or a conventional stepping motor, drives cylinder means 55 and 56 such that the endless belt 51 rotates in the direction E. A source of electrostatic developer particles, not shown, may be provided to supply the applicators 52, 53, 54 with such particles. The electrostatic developer particles are retained by the applicators in accordance with the triboelectric attraction between the fibers included in each of the applicators and the particles. When an applicator rotates into the vicinity of an electrostatic latent image such that the fibers of said applicator sweep over the electrostatic charge pattern, electrostatic forces between the charge pattern and the electrostatic particles are sufficient to urge said particles toward the charge pattern. Accordingly, developer particles are deposited on the electrostatic latent image and a visible iamge is developed. When the applicator now deficient in electrostatic developer particles advances to the source of electrostatic developer particles, the applicator is resupplied with developer particles. One advantage of the invention described herein is that if an electrostatic latent image is not adequately developed when an applicator such as applicator 54 passes thereover further development of the image is provided when a subsequent applicator such as applicator 53 sweeps over the image.

It should be recognized that the apparatus illustrated in FIG. may be utilized to develop an electrostatic latent image formed on a conventional electrophotographic member or on an insulating recording medium such as insulating recording medium'21 described with reference to FIG. 2. When the latter application is contemplated, an electrographic stylus such as aforedescribed electrographic stylus 24 is interposed between the endless belt 51 and the insulating recording medium. In addition, if lines of characters are to be recorded on the insulating recording medium the longitudinal dimension of each applicator 52, 53, 54 should be at least coextensive with the lateral dimension of the insulating recording medium, and the longitudinal axis of cylinder means 55 and 56 may be disposed in parallel relationship with respect to the surface of the insulating recording medium. One of ordinary skill in the art will now appreciate that an insulating recording medium may be particularly positioned such that if cylinder means 55 comprises a transparent cylinder and endless belt 51 comprises endless belt or a pair of oppositely disposed support members, an optical path representedby the arrow D may be established from an observer to a recorded character, which optical path passes through the endless belt 51 and cylinder means 55. The optical path will be periodically interrupted by the traversal of the applicators. For example,

as illustrated herein the optical pathD will first be interrupted by applicator 52 and then applicator 53. This periodic interruption produces the well-known flickering effect. However, the velocity of the applicators as well as the spacing therebetween and the width of each applicator may be particularly chosen such that the flickering effect is not readily noticeable by an observer.

The exemplary optical path D should not be interpreted as a limiting characteristic of the present invention. For example, the electrostatic latent image to be developed may be so positioned such that an optical path represented by the broken arrow D may be established from an observer to the recorded characters, such'that the optical path passes through the endless belt 51 at a point intermittent the cylinder means 55 and 56. In this case the endless belt 51 may comprise a transparent endless belt or a pair of oppositely disposed support members; however, the cylinder means 55 and 56 need not comprise transparent cylinders. Consideration should also be given to the positioning of the electrostatic latent image to be developed such that an optical path between an observer and a recorded character, represented by the broken arrow D", is established externally of the cylinder means 55 and 56. Observation of the recorded character along the optical path D", will be subject to the flickering effect; however, in this case the endless belt 51 need not comprise a transparent endless belt and cylinder means 55 and 56 need not be transparent cylinders.

The foregoing description of the embodiment illustrated in FIG. 5 has assumed that the longitudinal dimension of each applicator 52, 53, 54 may be coextensive with the lateral dimension of the insulating recording medium. Accordingly, FIG. 5 may be a side view of such embodiment. However, FIG. 5 may represent a top view of a further embodiment wherein the applicators 52, 53, 54 linearly traverse the insulating recording medium from one edge thereof to the other edge, in successive manner. Consequently, the longitudinal dimension of each applicator need only be slightly greater than the height of a line of characters. If the developing apparatus in accordance with this embodiment is to be utilized with the recording device illustrated in FIG. 2, for example, applicator 54 will scan an entire line on the surface of the insulating recording medium from the rightmost edge to the leftmost edge thereof. Applicators 53, 52 will successively scan the surface of the insulating recording medium in like manner. It is, of course, understood that if endless belt 51 rotates in a direction opposite to that indicated by the arrow E, the applicators 52, 53, 54 will successively scan an entire line on the surface of the insulating recording medium from the leftmost edge to the right most edge thereof.

A further modification of the developing apparatus of FIG. 5 is illustrated in FIG. 6 which comprises a moveable endless belt 61 deployed about a plurality of cylinder means 65, 66 and 67. A plurality of applicators 62, 63, 64 which are similar to aforedescribed applicators 52,53, 54 are mounted on the surface of endless belt 61. Endless belt 61 is similar to aforementioned endless belt 51. It should be readily understood that although three cylinder means 65, 66 and 67 are depicted in the embodiment of FIG. 6, any convenient number of cylinder means may be utilized. Thus the geometric configuration adopted by endless belt 61 is not limited solely to the triangular configuration of FIG. 6 but may assume a rectangular configuration, a pentagonal configuration, etc. The particular position ing of the illustrated cylinder means 65, 66 and 67 may be varied so as to alter the triangular configuration assumed by the endless belt 61, whereby the developing apparatus is readily adaptable to the precise nature of the support surface bearing the electrostatic latent image to be developed.

While the invention has been particularly shown and described with reference to exemplary embodiments thereof it will be obvious to those of ordinary skill in the art that the foregoing and various other changes and modifications in form and details may be made without departing from the spirit and scope of the invention. It is therefore intended that the appended claims be interpreted as including all such changes and modifications.

What is claimed is:

1. Apparatus for developing an electrostatic latent image comprising a transparent cylinder rotatable about the longitudinal axis thereof and a plurality of applicators capable of retaining electrostatic developer particles, said plurality of applicators being mounted in spaced relationship on said transparent cylinder such that said applicators sequentially contact said electrostatic latent image to deposit electrostatic developer particles thereon and an optical path passing through sadi transparent cylinder to a developed image is periodically interrupted by the rotation of said applicators.

2. The apparatus of claim 1 wherein said applicators comprise fibrous brushes longitudinally mounted on the surface of said transparent cylinder with substantially equal angles being defined between successive fibrous brushes, each of said fibrous brushes including fibers extending in a radially outward direction from said transparent cylinder.

3. Apparatus for developing an electrostatic latent image comprising a transparent endless belt moveable about a plurality of cylinder means and a plurality of applicators capable of retaining electrostatic developer particles, said plurality of applicators being mounted in spaced relationship on said transparent endless belt such that said applicators sequentially contact said electrostatic latentimage to deposit electrostatic developer particles thereon and periodically interrupt an optical path to a developed image, said optical path passing through said transparent endless belt when an applicator traverses said optical path.

4. The apparatus of claim 3 wherein said applicators comprise elongated fibrous brushes each having a longitudinal dimension substantially perpendicular to the direction of motion of said transparent endlessbelt with substantially equal spaces being defined between successive fibrous brushes, each fibrous brush including fibers extending in a normally outward direction from the surface of said transparent endless belt such that the terminal points of said fibers define a plane parallel to the surface of said transparent endless belt.

5. The apparatus of claim 4 wherein said optical path to a developed imageadditionally passes through one of said cylinder means.

6. Apparatus for printing characters on a print receiving surface comprising a transparent'cylinder having a longitudinal axis disposed in parallel relationship with respect to said print receiving surface,

stylus means for forming characters comprised of electrostatic charge patterns on said print receiving surface, said stylus means being interposed between said transparent cylinder and said print receiving surface and responsive to the selective energization thereof to deposit an electrostatic charge pattern on said print receiving surface in accordance with said selective energization, and

a plurality of applicators capable of retaining electrostatic developer particles, said plurality of applicators being mounted in spaced relationship on said transparent cylinder such that said applicators sequentially contact said print receiving surface to deposit electrostatic developer particles on said electrostatic charge patterns,

said transparent cylinder being rotatable about said longitudinal axis such that an optical path passing through said transparent cylinder to a printed character is periodically interrupted by the rotation of said applicators.

7. The apparatus of claim 6 wherein said applicators comprise fibrous brushes longitudinally mounted on the surface of said transparent cylinder with substantially equal angles being defined between successive fibrous brushes,'each of said fibrous brushes including fibers extending in a radially outward direction from said transparent cylinder.

'8. The apparatus of claim 7 wherein said transparent cylinder is substantially coextensive with the lateral dimension of said print receiving surface.

9. The apparatus of claim 8 wherein said stylus means and said print receiving surface are disposed for relative lateral displacement therebetween.

10. Apparatus for printing characters on a print receiving surface comprising a transparent endless belt having a surface moveable abouta plurality of cylinder means in a plane disposed in spaced registration from said print receiving surface,

stylus means for'forming characters comprised of electrostatic charge patterns on said print receiving surface, said stylus means being interposed between said transparent endless belt and said print receiving surface and responsive to the selective energization thereof to deposit an electrostatic charge pattern on said print receiving surface in accordance with said selective energization, and

a plurality of applicators capable of retaining electrostatic developer particles, said plurality of applicators being mounted in spaced relationship on said transparent endless belt such that said applicators sequentially contact said print receiving surface to deposit electrostatic developer particles on said electrostatic charge patterns,

at least two of said cylinder means having their respective longitudinal axis disposed in parallel relationship with respect to said print receiving surface such that an optical path to a printed character passes through said transparent endless belt and is periodically interrupted by the movement of said applicators.

11. The apparatus of claim 10 wherein said applicators comprise elongated fibrous brushes each having a longitudinal dimension substantially perpendicular to the direction of motion of said transparent endless belt with substantially equal spaces being defined between successive fibrous brushes, each fibrous brush including fibers extending in a normally cutward direction from the surface of said transparent endless belt such that the terminal points of said fibers define a plane parallel to the surface of said transparent endless belt.

12. The apparatus of claim 1 wherein the width of said transparent endless belt is substantially coextensive with the lateral dimension of said print receiving surface.

13. The apparatus of claim 12 wherein said stylus means and said print receiving surface are disposed for relative lateral displacement therebetween. 

1. Apparatus for developing an electrostatic latent image comprising a transparent cylinder rotatable about the longitudinal axis thereof and a plurality of applicators capable of retaining electrostatic developer particles, said plurality of applicators being mounted in spaced relationship on said transparent cylinder such that said applicators sequentially contact said electrostatic latent image to deposit electrostatic developer particles thereon and an optical path passing through sadi transparent cylinder to a developed image is periodically interrupted by the rotation of said applicators.
 2. The apparatus of claim 1 wherein said applicators comprise fibrous brushes longitudinally mounted on the surface of said transparent cylinder with substantially equal angles being defined between successive fibrous brushes, each of said fibrous brushes including fibers extending in a radially outward direction from said transparent cylinder.
 3. Apparatus for developing an electrostatic latent image comprising a transparent endless belt moveable abOut a plurality of cylinder means and a plurality of applicators capable of retaining electrostatic developer particles, said plurality of applicators being mounted in spaced relationship on said transparent endless belt such that said applicators sequentially contact said electrostatic latent image to deposit electrostatic developer particles thereon and periodically interrupt an optical path to a developed image, said optical path passing through said transparent endless belt when an applicator traverses said optical path.
 4. The apparatus of claim 3 wherein said applicators comprise elongated fibrous brushes each having a longitudinal dimension substantially perpendicular to the direction of motion of said transparent endless belt with substantially equal spaces being defined between successive fibrous brushes, each fibrous brush including fibers extending in a normally outward direction from the surface of said transparent endless belt such that the terminal points of said fibers define a plane parallel to the surface of said transparent endless belt.
 5. The apparatus of claim 4 wherein said optical path to a developed image additionally passes through one of said cylinder means.
 6. Apparatus for printing characters on a print receiving surface comprising a transparent cylinder having a longitudinal axis disposed in parallel relationship with respect to said print receiving surface, stylus means for forming characters comprised of electrostatic charge patterns on said print receiving surface, said stylus means being interposed between said transparent cylinder and said print receiving surface and responsive to the selective energization thereof to deposit an electrostatic charge pattern on said print receiving surface in accordance with said selective energization, and a plurality of applicators capable of retaining electrostatic developer particles, said plurality of applicators being mounted in spaced relationship on said transparent cylinder such that said applicators sequentially contact said print receiving surface to deposit electrostatic developer particles on said electrostatic charge patterns, said transparent cylinder being rotatable about said longitudinal axis such that an optical path passing through said transparent cylinder to a printed character is periodically interrupted by the rotation of said applicators.
 7. The apparatus of claim 6 wherein said applicators comprise fibrous brushes longitudinally mounted on the surface of said transparent cylinder with substantially equal angles being defined between successive fibrous brushes, each of said fibrous brushes including fibers extending in a radially outward direction from said transparent cylinder.
 8. The apparatus of claim 7 wherein said transparent cylinder is substantially coextensive with the lateral dimension of said print receiving surface.
 9. The apparatus of claim 8 wherein said stylus means and said print receiving surface are disposed for relative lateral displacement therebetween.
 10. Apparatus for printing characters on a print receiving surface comprising a transparent endless belt having a surface moveable about a plurality of cylinder means in a plane disposed in spaced registration from said print receiving surface, stylus means for forming characters comprised of electrostatic charge patterns on said print receiving surface, said stylus means being interposed between said transparent endless belt and said print receiving surface and responsive to the selective energization thereof to deposit an electrostatic charge pattern on said print receiving surface in accordance with said selective energization, and a plurality of applicators capable of retaining electrostatic developer particles, said plurality of applicators being mounted in spaced relationship on said transparent endless belt such that said applicators sequentially contact said print receiving surface to deposit electrostatic developer particles on said electrostatic charge patterns, at least two of said cylinder means having their respective longitudinal axis disposed in parallel relationship with respect to said print receiving surface such that an optical path to a printed character passes through said transparent endless belt and is periodically interrupted by the movement of said applicators.
 11. The apparatus of claim 10 wherein said applicators comprise elongated fibrous brushes each having a longitudinal dimension substantially perpendicular to the direction of motion of said transparent endless belt with substantially equal spaces being defined between successive fibrous brushes, each fibrous brush including fibers extending in a normally cutward direction from the surface of said transparent endless belt such that the terminal points of said fibers define a plane parallel to the surface of said transparent endless belt.
 12. The apparatus of claim 1 wherein the width of said transparent endless belt is substantially coextensive with the lateral dimension of said print receiving surface.
 13. The apparatus of claim 12 wherein said stylus means and said print receiving surface are disposed for relative lateral displacement therebetween. 